From a point of view of lowering in on resistance, a contact resistance between a silicon carbide semiconductor layer and an electrode is preferably lower in a silicon carbide semiconductor device containing silicon carbide (SiC) as a semiconductor material.
In order to lower a contact resistance between the silicon carbide semiconductor layer and the electrode, in general, a contact region high in impurity concentration is formed in the silicon carbide semiconductor layer. For example, when the silicon carbide semiconductor device is implemented as an MOSFET, a well region is formed in the silicon carbide semiconductor layer, and a source region and a contact region in contact with the source region and high in impurity concentration are formed in the well region.
Since silicon carbide is extremely low in coefficient of diffusion of an impurity, doping with an impurity through a thermal diffusion process is difficult. Therefore, ion implantation or epitaxial growth has been used for forming an active region in a method of manufacturing a silicon carbide semiconductor device.
WO2009/139140 describes a silicon carbide semiconductor device in which a p+ type contact region is formed to be deeper than a source region located around the same. The p+ contact region is formed through ion implantation.